The likely cause of Friday’s Metro derailment on the Silver Line was a track defect called “wide gauge,” which causes the wheels to lose contact with the rails as a result of old infrastructure.

It’s the same problem that caused a non-passenger train to come off the tracks last August as an operator was preparing to start service at the Smithsonian station.

Metro said car equipment, weather conditions, heat and other factors may have played into Friday’s derailment just outside East Falls Church. But a preliminary assessment showed that the tracks were too wide to support the train because of deteriorated rail ties, the wooden slabs that secure the running rail.

“At this time there is no evidence of train operator error,” the agency said in a news release.

The derailment on Friday led to at least one injury and the evacuation of 60 passengers. It caused service to be suspended on a western portion of the Orange and Silver lines through Monday morning.

Over the weekend, Metro said, more than 450 rail ties were replaced in the area of the derailment, which hadn’t been part of the SafeTrack project repairs that were underway between Ballston and East Falls Church.

General Manager Paul J. Wiedefeld ordered special inspections of all the system’s tracks “to look for any other similar conditions that must be immediately addressed,” he said in a statement.

The transit agency also conducted early inspections of Red Line interlockings before launching SafeTrack surge No. 6 on Monday morning. Friday’s derailment occurred while a train was passing through an interlocking.

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